Thread cutting mechanisms for sewing machines



'Jan. 17, 1961 D. 6. SMITH EF AL 2,968,269

THREAD CUTTING MECHANISMS FOR SEWING MACHINES Filed June 24, 1959 Y 2 Sheets-Sheet 1 Darwin 6. Smith and BY .SIanIey J. Kellerer.

AT TORZVEY Jan. 1-7, 1961 D. G. SMITH ETAL 2,968,269

THREAD CUTTING MECHANISMS FOR SEWING MACHINES Filed Juhe 24, 1959 2 Sheets-Sheet 2 INVENTORS. 1 1 63 Darwin 6. .Smifh and BY Stanley J. Keflerer.

Fig.7. W

THREAD CUTTING MECHANISMS FOR SEWING MACHINES Darwin G. Smith, Bridgeport, and Stanley J. Ketterer,

Stratford, Conn., assignors to The Singer Manufacturing Company, Elizabeth, N.J., a corporation of New Jersey Filed June 24, 1959, Ser. No. 822,577

13 Claims. (Cl. 112-252) This invention relates to thread cutting mechanisms for sewing machines and, more particularly, to mechanisms for severing and holding the severed end of the under thread in a two-thread sewing machine.

It is an object of this invention to provide an im-' companying drawings of a preferred embodiment in which:

Fig. 1 represents a bottom plan view of that portionof a sewing machine bed beneath the stitching point with the loop taker broken away to expose the thread severing instrumentalities,

Fig. 2 represents an enlarged bottom plan view of the thread severing instrumentalities of Fig. 1,

Fig. 3 represents a cross-sectional view taken substantially along line X-X of Fig. 1, including fragments of the work fabrics, thread, and loop taker with the parts occupying the position illustrated in Fig. 1,

Figs. 4-7 represent enlarged cross-sectional views taken substantially along line X-X of Fig. 1, and showing the thread severing and nipping mechanisms in successive critical positions during a typical operating cycle, thereof, and in which 1 Fig. 4 illustrates the position of the parts when the thread carrying member first engages the thread nipping finger,

Fig. 5 illustrates the position of parts at the instant of thread severing,

Fig- 6 illustrates the position'of parts at the extreme position in the thread cutting direction in which the thread carrying member has fallen behind the thread nipping finger, I r

Fig. 7 illustrates the position of parts after the thread cutter and thread nipper have completed their operative motion,

Fig. 8 represents a top plan view of the knife blade,

Fig. 9 represents a top'plan' view of the thread carrying finger,

ence may be had for a complete understanding of its operation.

Briefly, 11 indicates the sewing machine bed transversely across which is arranged a slide plate 12 endwise shiftable by a lever 13 actuated by a pattern cam 14. Slidably arranged for movement lengthwise of the machine bed in ways 15 secured on the slide plate 12 is the work supporting plate 16 of a work holder influenced by a link 17 operated by the cam 14. A throat plate 18 secured to the slide plate 12 and slidably embraced by the work supporting plate 16 is formed 4 with a laterally elongated needle hole 19 which has opening into it a narrow slot 20 lengthwise of the bed through which the buttonhole is cut in the work fabric.

In the sewing of a buttonhole, by the machine illustrated in the drawings, the sewing machine needle (not shown) is jogged to provide the zigzag stitches of the buttonhole, the slide plate 12 is shifted by the lever 13 to space the lines of zigzag stitches on opposite sides of the buttonhole, and the work supporting plate 16 is shifted by the link 17 to carry the work fabric lengthwise thus determining the length of the buttonhole.

Journ led in bearings beneath the bed 11 is a loop taker drive shaft 30 which imparts circular movement in timed relation with the needle to a loop taker 31, a portion of the latter being illustrated in Fig. 3. The loop taker is of the type referred to in theart as a rotary hook, having a thread engaging beak for carrying loops of needle thread about a mass of under thread carried on a bobbin (not shown) lodged within the rotary hook.l The concatination of loops of needle thread, indicated at N in Figs. 3-7, with the bobbin thread B provides locked stitches in the work.

. in Figs. 13, and the bobbin thread B will extend from' Fig. 10 represents a top plan view of the camming blade,

Fig. 11 repre ents a top plan view of the ledger blade,

, Fig. 12 represents a top plan view of the thread nipping vblade, and

the work to the bobbin within the loop taker 31. Notonly must the bobbin thread be severed between the work and the bobbin, but also, control of the bobbin thread must be maintained such that it will be incorporated properly into the next buttonhole to be stitched. For the purpose of operating the thread cutting and.

nipping mechanism of this invention, a lever 40 is fulcrumed beneath the sewing machine bed and is oscillated by a cam means (not shown) associated with the mechani m for stopping the sewing machine upon completion of the buttonhole, as described in detail in the above referenced Allen Patent No. 1,559,539. A spring 41 serves to assist in returning the lever 40 to the at rest position illustrated in Fig. l.

The lever 40 is bifurcated and embraces a pin 42 depending from a knife carrier bar 43 slidably constrained in the sewing machine bed 11 beneath the slide plate 12 for endwise movement transversely across the bed. Secured to the carrier bar 43 by screws 44 is a bracket 45 to which a group of thread manipulating instrumentalities including a knife blade 46, a thread carrying finger 47, and a thread camming blade 48 are secured by a single fastening screw 49. As illustrated in Figs. 2 and 8, the knife blade 46 is formed with a sharpened cutting edge 50 and with a beveled camming edge 51. The thread carrying finger 47, illustrated in Fig. 9, is formed with a concave threadpositioning notch 52 disposed in front of the cutting edge 50 of the knie blade. shown in Fig. 10, is formed with an inclined leading edge 53 which slopes toward the thread positioning notch 52 of the thread carrying finger 47 to urge the bobbin thread into the notch 52.

Opposed to and cooperating with the three thread manipulating instrumentalities 46,47, and 48, carried on the knife carrier bar are a group of thread manipulating Patented Jan. 17, 1961 The camming blade 48,-

instrumenta ities fixed on the ways of the slide plate 12. Secured in the plate on the ways 15 by fastening screws 60 and 68 is a ledger blade 62, illustrated in Fig. 11, which also serves as an abutment element against which a thread nipping blade 63 presses. The thread nipping blade 63 illustrated in Fig. 12 is secured on the screw 60 by way of an eccentric sleeve 61. The eccentric sleeve 61 provides a means for seating the thread nipping blade snugly against the side wall of an aperture 64 formed in the slide plate 12. The ledger blade 62 is formed with a cutting edge 65 cooperating with the cutting edge 50 of the kni e blade 46, and is formed with a beveled finger or pilot 66 cooperating with the camming edge 51 of the knife blade 46 to guide the knife blade properly with respect to theledger blade. i V

The thread nipping blade 63 is formed with a lateral thread nipping finger 67 which extends across and abuts the ledger blade behind the cutting edge 65 thereof.

Secured in place on the ways 15 by the screw 68 is a leaf spring 69 which, as illustrated in Fig. 13, is formed with a struck up dimple 70 and with a lateral finger 71 which underlies the lateral thread nipping finger 67 and urges the lateral finger 67 upwardly against the abutment element provided by the ledger blade.

Figs. 4-7 illustrate the sequence of events during an oscillation of the lever 40 and the consequent reciprocation of the knife carrier bar 43. As illustrated in Fig. 4, the thread carrying finger 47 first engages the outer edge of the thread nipping finger 67, the thread B having been directed by the camming blade 48 into the thread positioning notch 52 of the thread carrying finger. The outer edge of the thread nipping finger 67 is beveled upwardly toward the ledger blade 62 so as to urge the thread carrying finger 47 upwardly and between the thread nipping; 35

finger 67 and the ledger blade.

As illustrated in Fig. 5, continued motion of the assembly comprising the blades 46, 47, and 48 will cause the thread carrying finger 47 to draw a loop of bobbin thread between the ledger blade 62 and the thread nipping finger 67. The knife blade 46 will, at the same time, be cammed upon the ledger blade 62 by the cooperation of the cam surface 51 on the knife blade and the beveled edge of the finger 66 on the ledger blade. As the cutting edges 50, 65 move together, the bobbin thread B, while being held taut by the nipping action of the thread nipping finger 67, will be cut cleanly by the shearing action of the blades 46 and 62.

Illustrated in Fig. 6 is the extreme position of the movable blades 46, 47, and 48. The thread has been severed and the thread carrying finger 47 has dropped behind the thread nipping finger 67. The leaf spring 69 will immediately urge the thread nipping finger toward the ledger blade 62 to grip the bobbin thread deposited therebetween by the thread carrying finger.

The inner edge of the thread nipping finger 67 as well as the inner edge of the thread carrying finger 47 are beveled downwardly and toward the leaf spring 71 such that, as the knife carrying bar 43 is returned, the thread carrying finger 47 will be urged downwardly between the thread nipping finger 67 and the lateral finger 71 of the leaf spring 69. The severed end of the bobbin thread B will thus be carried between the nipping finger 67 and the finger 71 of the leaf spring so that the thread will be wrapped completely around the thread nipping finger 67 and will be gripped twice, i.e., between the finger 67 and the ledger blade 62. and between the finger 67 and the extension 71 of the spring.

Also of importance is the fact that in the operation of the cutting and nipping device of this invention, the thread carrying finger 47 travels in only one direction between any given set of thread nipping elements. This invention thus obviates the disadvantage of the prior, art constructions in which the thread carrier is withdrawn from between the nipping elements in a direction opposite that in which it is inserted and, therefore, tends to with 4 draw the thread as well. Nipping with the device of this invention is accomplished in a positive, dependable man-' ner.

At the start of stitching onthe succeeding buttonhole, the bobbin thread remains nipped as illustrated in Fig. 7. Referring to Figs. 1 and 2, 'it willbe appreciated that the work supporting plate16 will be advanced by the link 17 during the stitching operations. The work supporting plate 16 is formed in the underside with a pair of grooves 75 and 76, which grooves are aligned with the struck up dimple 70 in the leaf spring 69. The short groove 75 is disposed to accommodate the dimple when the parts occupy an at rest position at the start and completion of sewing. After a predetermined number of stitches have been formed and the bobbin thread has been anchored in the work by the formation of these stitches, the work supporting plate 16 will be shifted sufficiently to shift the groove 75 out of registry with the dimple 70. As the dimple is engaged by the raised land between the grooves 75 and 76, the spring will be urged downwardly and out of engagement with the thread nipping finger 67 thereby releasing the bobbin thread B which will be drawn off the finger 67. Once the thread has been released, there is no further need for the spring pressure on the nipping finger 67 until the completion of the stitching, however, the. groove 76 is provided in order to reduce the frictional drag which would otherwise be occasioned by the dimple.

70 being drawn against the underside of the work supporting plate.

Having set forth the nature of this invention what is.

claimed is:

1. A sewing machine thread cutting and nipping device, comprising opposed thread manipulating instrumentah. ittes, a thread cutting blade carried by one of said in-.

strumentalities, one of said instrumentalities including an abutment element, a thread nipping finger disposed contiguous to said abutment element, and means for biasing said thread nipping finger against said abutment element, I

forth relatively to the other, and means for directing said thread carrying finger between the nipping finger and the abutment element during relativev movement of said instrumentalities in one direction, and to one side of both said nipping finger and said abutment element during relative movement of said instrumentalities in the opposite direction.

2. A sewing machine thread cutting and nipping device comprising opposed thread manipulating instrumentalities, a thread cutting blade carried by one of said instrumentalities, one of said instrumentalities including an abutment element, a thread nipping finger disposed contiguous to said abutment element, and means for biasing said thread nipping finger against said abutment element, the opposing instrumentality including a thread carrying finger, means for supporting said instrumentalities in retracted positions on opposite sides of the thread to be nipped and severed, means for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger on that side of the nipping finger which is contiguous to the abutment element during rela- .tive movement of said instrumentalities in one direction,

abutment. element, a thread nipping finger disposed cone tiguous'to said abutment element, and a spring means engaging and biasing said thread nipping finger against said abutment element, the opposing instrumentality in-- cluding a thread carrying finger, means for supporting said instrumentalities in retracted positions on opposite sides of the thread to be nipped and severed, means for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger between the nipping finger and the abutment element during relative movement of said instrumentalities in one direction, and between the nipping finger and said spring means during relative movement of said instrumentalities in the opposite direction.

4. A sewing machine thread cutting and nipping device comprising opposed thread manipulating instrumentalities, cooperating thread cutting blades carried one by each of said opposed instrumentalities, one of said instrumentalities including a thread nipping finger disposed contiguous to said thread cutting blade thereon, and means for biasing said thread nipping finger against said thread cutting blade, the opposing instrumentality ineluding a thread carrying finger, means for supporting said instrumentalities in retracted positions on opposite sides of the thread to be nipped and severed, means for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger between the nipping finger and the contiguous thread cutting blade during relative movement of said instrumentalities in'one direction, and to one side of both said nipping finger and said contiguous thread cutting blade during relative movement of said instrumentalities in the opposite direction.

5. A sewing machine thread cutting and nipping device comprising a ledger blade, a thread nipping finger disposed contiguous to said ledger blade, means for biasing said thread nipping finger against said ledger blade, and means for securing said elements together at one side of the thread to be nipped and severed, a carrier member shiftably supported on said sewing machine, a thread cutting blade, a thread carrying finger, and means for securing said thread cuttingblade and said thread carrying finger to said carrier member in a position located at the opposite side of the thread to be nipped and severed when the carrier member occupies a retracted position, means for shifting said carrier member to reciprocate said thread cutting blade and said thread carrying finger back and forth past said ledger blade and said thread nipping finger, and means for directing said thread carrying finger between the thread nipping finger and the ledger blade during movement of said carrier member in one direction, and to one side of both said thread nipping finger and said ledger blade during relative movement of said carrier member in the opposite direction.

6. A thread cutting and nipping device as set forth in claim 5, in which said thread carrying and thread nipping fingers are disposed for operative engagement to nip the thread prior to operative thread severing engagement of the thread cutting blade with the ledger blade.

7. A device as set forth in claim 5 in which the thread carrying finger is formed with a thread positioning notch and in which a thread camming blade is secured to said carrier member and formed with an inclined leading edge directed toward the thread positioning notch of said thread carrying finger.

8. A thread cutting and nipping device as set forth in claim 1 and in which said thread nipping and thread carrying fingers each extend laterally of the direction of reciprocatory movement of said instrumentalities and said fingers each have oppositely extending free extremities.

9. A thread cutting and nipping device as set forth in claim 8 in which the means for directing the thread carstantially the same inclination.

10. A thread cutting and nipping device for a cyclic sewing machine having a stop motion mechanism, said device comprising opposed thread manipulating instru' mentalities, a thread cutting blade carried by one of said instrumentalities, one of said instrumentalities including an abutment element, a thread nipping finger disposed contiguous to said abutment element, and means for bias? ing said thread nipping finger against said abutment element, the opposing instrumentality including a thread carrying finger, means for supporting said instrumentalities in retracted positions on opposite sides of the thread to be nipped and severed, means actuated during operation of said stop motion device for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger between the nipping finger and the abutment element during relative movement of said instrumentalities in one direction and to one side of both said nipping finger and said abutment element during relative movement of said instrumentalities in the opposite direction, and means effective upon completion of a predetermined number of stitches in one cycle of stitching for releasing said means that biases said thread nip ping finger against said abutment member.

11. A thread cutting and nipping device for the bobbin thread of a lock stitch sewing machine comprising opposed thread manipulating instrumentalities disposed beneath the sewing machine stitching point, a thread cutting blade carried by one of said instrumentalities, one of said instrumentalities including an abutment element, a thread nipping finger disposed contiguous to said abutment element, and means for biasing said thread nipping finger against said abutment element, the opposing instrumentality including a thread carrying finger, means for supporting said instrumentalities in retracted positions on opposite sides of the bobbin, means for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger between the nipping finger and the abutment element during relative movement of said instrumentalities in one direction, and to One side of both said nipping finger and said abutment element during relative movement of said instrumentalities in the opposite direction.

12. A thread cutting and nipping device for the bobbin thread of a lock stitch sewing machine having a work supporting bed, comprising opposed thread manipulating instrumentalities disposed beneath said bed, one of said instrumentalities comprising an assembly carried as a unit beneath said bed and including a ledger blade adjoining said bed, a thread nipping finger secured beneath and contiguous to said ledger blade, and a leaf spring beneath said thread nipping finger biasing said finger upwardly against said ledger blade, the opposing instrumentality comprising an assembly carried as a unit beneath said bed and including a thread cutting blade adjoining said bed, a thread carrying finger secured beneath said thread cutting blade and formed with a thread positioning notch, and a thread camming blade secured beneath said thread carrying finger and formed with an inclined leading edge extending beneath said thread positioning notch, means for supporting said instrumentalities in retracted position on opposite sides of the bobbin thread, means for reciprocating one of said opposed thread manipulating instrumentalities back and forth relatively to the other, and means for directing said thread carrying finger between the thread nipping finger and the ledger blade during relative movement of said instrumentalities in one direction, and between said thread nipping finger and said leaf spring during rela tive movement of said instrumentalities in the opposite direction.

13. A thread cutting and nipping device for the bobbin 7" thd:. -a: 1@k stit hbu te ql ew nsv-m hingWm: m nc nh x q stit w h w bun fo med m h prising a device as set forth in claim. 12 supported b lfionholfi.

sneas 1 wQ k. holdc; f th e n mac ,1 which figs: mg lgngighr of: the buttonhole in the Stitching References Cited; in the file of this patent thswof, in hi hflth eaf sw n i fq med h n ofi 4 I E STATES N S mp m p se zi hapa h of r el of ac m trac 1,930, 7 Allen ct, 17, 1 3,- fgrmed on-thevsewingimachine work holdr, said cam 2, 7 ,417 chudnerr May 22, 1945; track being formed to release-the tension exerted by the- 2,474,710 w q Jun 2 194 9 leafspring on the thread nipping finger after a'predgter: 2,707,927 Artzt et a1. May 10, 1 955 

